Note: Descriptions are shown in the official language in which they were submitted.
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ROTARY COMPRESSOR
BACKGROUND
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit under Title 35, U.S.C. 119(e) of
U.S. Provisional
Patent Application Serial No. 61/246,319, filed September 28, 2009, titled
ROTARY
COMPRESSOR, the disclosure of which is expressly incorporated herein by
reference.
1. Field of the Invention
[0002] The present invention relates to compressors and, particularly, to
rotary compressors.
2. Description of the Related Art.
[0003] In a rotary compressor, the compression mechanism includes an eccentric
positioned
within a cylindrical compression chamber. A vane extending from the
cylindrical wall of the
compression chamber contacts a roller positioned around the eccentric and
divides the
compression chamber into compression and suction pockets. As the eccentric
and,
correspondingly, the roller move through the compression chamber, the
compression pocket
decreases in volume to compress a working fluid contained therein. At the same
time, the
suction pocket is increasing in volume and drawing working fluid into the
suction pocket. As the
eccentric and roller continue to rotate, the portion of the roller contacting
the wall of the
compression chamber passes by the vane. When this occurs, the suction pocket
becomes the
compression pocket.
[0004] Due to the rotation of the eccentric through the compression mechanism,
a
counterweight must be used to keep the crankshaft and other components of the
compressor in
balance. However, as the size of the rotary compressor increases, the size of
the eccentric and its
corresponding counterweight also increase. Additionally, in order to obtain
proper balance, two
counterweights may be used. For example, in some rotary compressors, a first
counterweight is
positioned at the end of the crankshaft opposite the eccentric and on the same
side as the
eccentric, while a second counterweight is position between the eccentric and
the first
counterweight on the opposite side of the crankshaft as the eccentric and the
first counterweight.
In order for the second counterweight to effectively balance the system, the
mass-eccentricity of
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the second counterweight must be equal to the sum of the mass-eccentricities
of the first
counterweight and the eccentric and the roller. Thus, as rotary compressors
increase in volume,
i.e., provide compression in the range of 5 to 10 tons, the eccentrics and
corresponding
counterweights also increase in size. As a result, the size of the
counterweights make both the
design and assembly of such a compressor increasingly difficult. For example,
the height of the
compressor must be increased to provide room for the counterweights and the
counterweight
attachments must be made stronger to accommodate increased centrifugal forces.
SUMMARY
[0005] The present invention relates to compressors and, particularly, to
rotary compressors.
In one exemplary embodiment, the eccentric on the crankshaft of a rotary
compressor, as well as
the roller that surrounds the eccentric, is replaced by an elongated,
preferably elliptical, cam that
acts as a double eccentric. In this manner, the elliptical cam provides for
inherent balancing of
the crankshaft and other components of the compressor, eliminating the need to
use
counterweights. Specifically, the elliptical cam is symmetrical, resulting in
equal inertial forces
acting on opposing sides of the elliptical cam. This allows the elliptical cam
to maintain its
balance throughout its rotation, even when operating at a high rate of
revolution. Additionally,
because pressure forces from the compression pockets are equal and opposite in
direction,
bearing loads are reduced which allows for the use of a smaller bearing. This,
in turn, reduces
the viscous frictional losses associated with shearing of oil in the bearings,
which increases
mechanical efficiency.
[0006] Advantageously, eliminating the use of counterweights in the rotary
compressor of the
present invention decreases the overall height and size of the compressor.
Additionally, it
allows for the rotary compressor to be utilized to compress larger volumes of
working fluid and
also eliminates the need to provide a roller surrounding an eccentric on the
crankshaft.
[0007] In another exemplary embodiment, the present invention includes an open
suction
pressure channel that extends along an inner surface of the compression
mechanism of the
compressor to draw suction pressure working fluid into the opposing working
pockets defined by
the elliptical cam. In another exemplary embodiment, a cross passage is formed
through the
elliptical cam to draw suction pressure working fluid into the opposing
working pockets defined
by the elliptical cam. By utilizing the open suction pressure channel and/or
the cross passage of
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the present invention, a single suction port may be provided in the
compression mechanism to
draw suction pressure working fluid into both working pockets of the
compression mechanism.
[0008] Additionally, in one exemplary embodiment, the outboard journal bearing
is eliminated
and the crankshaft of the compressor includes only a single journal bearing,
i.e., the main
bearing, which is positioned between the cylinder and the motor. Elimination
of the outboard
journal reduces the viscous friction losses of the compressor and increases
mechanical
efficiency. Also, because the outboard journal consists of precisely machined
surfaces, its
elimination reduces the cost of manufacturing the compressor.
[0009] In one form thereof, the present invention provides a rotary compressor
having an outer
hermetic housing, a motor and a cylinder having an inner cylindrical surface
including a plurality
of slots formed therein, the inner cylindrical surface defining a
substantially cylindrical bore. A
crankshaft includes an elongate cam, either integral therewith or attached
thereto, which is
rotatably disposed within the cylinder block such that the outer surface of
the elongate cam
contacts the inner cylindrical surface of the cylinder block at two
circumferentially spaced
positions to form a pair of working pockets. First and second vanes are
positioned at least
partially within the slots in the cylinder block and biased inwardly to
contact the outer surface of
the elongate cam. An outboard thrust bearing is positioned adjacent the
cylinder block and a
main bearing positioned adjacent the cylinder block at an axial end thereof
and at least partially
defining a discharge port in fluid communication with the working pockets at
certain rotation
angles of the elongate cam. A suction pressure inlet is in communication with
the working
pockets at certain angles of rotation of the cam to supply suction pressure
working fluid into the
working pockets.
[0010] In another form thereof, the present invention provides a rotary
compressor having an
outer hermetic housing, a motor and a cylinder having an inner cylindrical
surface including a
plurality of slots, the inner cylindrical surface defining a substantially
cylindrical bore. A
crankshaft having an elongate cam thereon is rotatably disposed within the
cylinder block such
that the outer surface of the cam contacts the inner surface of the cylinder
block at two
circumferentially spaced positions to form a pair of working pockets. First
and second vanes at
least partially positioned within the slots are biased inwardly to contact the
outer surface of the
elongate cam. An outboard thrust bearing is positioned adjacent the cylinder
block and defines a
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suction pressure passage therein, the suction pressure passage in simultaneous
fluid
communication with each of the working pockets at certain rotation angles of
the cam to draw
suction pressure working fluid from a suction pressure inlet to both of the
working pockets. A
main bearing is provided adjacent the cylinder and at least partially defines
a discharge port in
fluid communication with the working pockets at certain rotation angles of the
elongate cam.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The above-mentioned and other features and advantages of this
invention, and the
manner of attaining them, will become more apparent and the invention itself
will be better
understood by reference to the following description of an embodiment of the
invention taken in
conjunction with the accompanying drawings, wherein:
[0012] Fig 1 is a perspective view of a rotary compressor in accordance with
an embodiment
of the present invention;
[0013] Fig. 2 is a plan view thereof;
[0014] Fig. 3 is a sectional view thereof taken along one A-A of Fig. 2 and
viewed in the
direction of the arrows, wherein the section is taken through the suction
port;
[0015] Fig. 4 is a sectional view thereof taken through the vanes;
[0016] Fig. 5 is a sectional view thereof taken through the discharge ports;
[0017] Fig. 6 is a transverse sectional view of the compressor taken through
the cylinder;
[0018] Fig. 7 is a perspective view of the outboard thrust bearing showing the
suction panel
[0019] Fig. 8 is a perspective view of the main bearing;
[0020] Fig. 9 is a perspective view of an alternative crankshaft and cam
design; and
[0021] Fig. 10 is a sectional view of the alternate embodiment.
DETAILED DESCRIPTION
[0022] Fig. 1 illustrates the rotary compressor 10 forming one embodiment of
the present
invention. Compressor 10 includes an outer hermetic housing 12 including
center portion 14 to
which upper and lower caps 16 and 18 are connected, such as by welding. A
conventional
suction accumulator 20 having inlet 22 and outlet suction line 24 is connected
to the center
portion 14 of compressor 10 by means of mounting strap 26. Compressed
refrigerant is
discharged from high pressure housing 12 through discharge line 28. Compressor
10 may be a
component of a heating and/or cooling circuit and functions to compress the
working fluid, such
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as a refrigerant, which may be a hydrofluorocarbon, chlorofluorocarbon,
hydrochlorofluorocarbon, or carbon dioxide refrigerant, for example.
[0023] Turning now to Figs. 3-5, motor 30 and compression mechanism 32 are
mounted
within hermetic housing 12. Oil sump 41 (Fig. 3) is formed in the lower
portion of hermetic
housing 12. The motor includes stator 34 and rotor 36. Compression mechanism
32 comprises a
cylinder 34 that is rigidly connected to the inner surface 35 of housing
center section 14, a main
bearing 36 fastened to cylinder 34 by means of a plurality of screws 38 and an
outboard thrust
bearing 40 connected to cylinder 34 by means of a plurality of screws 42.
Suction line 24
extends through the center section 14 of housing 12 and is sealably joined to
cylinder block 34 in
communication with suction port 44 which opens into the wall of cylinder bore
50.
[0024] An elongate cam 46, which is preferably elliptical, is preferably
integrally connected
with crankshaft 14, although alternatively it may be a separate element
connected by any suitable
means. Shaft 64 is rotationally secured to rotor 28 and, as shown in Fig. 6,
cam 46 is in sealing
engagement with the bore 50 of cylinder 34.
[0025] Extending through elliptical cam 46 and up through shaft 48 is oil
passage 52. Oil
paddle 54 extends from oil passage 52 of elliptical cam 46 and is configured
to draw oil upward
and into passageway 52 that is in combination with passages 56 in elliptical
cam 46. Passages 56
extend through elliptical cam 46 and direct oil into main bearing 36 between
elliptical cam 46
and rotor 28 of motor 30. In order to advance the oil further along the
journal surface of
crankshaft 48 and substantially entirely along main bearing 36, the journal
surface of crankshaft
48 may include a spiral groove (not shown). Alternatively, passages 56 may
extend into
crankshaft 48 and exit crankshaft 48 at a point above main bearing 36 allowing
oil exiting
passages 56 to pass along the journal surface and through main bearing 36. For
example,
passages 56 may be in fluid communication with radial discharge passages (not
shown) that are
positioned above or within main bearing 36. Alternatively, oil passage 52 may
extend through
the entire length of crankshaft 48 as shown. Oil passage 92 extends from the
oil passage 52 of
crankshaft 48 to the outboard thrust bearing surface of thrust bearing 40.
[0026] Referring to Fig. 6, slots 58 are formed in cylinder block 34 and have
vanes 60
positioned therein. Springs 62 bias vanes 60 radially inwardly toward the
center of cylinder 34
during start-up of the compressor. After start-up, discharge pressure working
fluid is used to
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bias vanes 60 radially inwardly. Cylinder 34 includes an inner cylindrical
surface defining
cylinder bore 50 for rotation of elliptical cam 46 therein.
[0027] By utilizing elliptical cam 46, the need for a roller is eliminated. As
a result, any
potential wear that may occur between the contact surfaces of the roller and
an eccentric is also
eliminated. Additionally, elliptical cam 46 is symmetrical and provides for
proper balancing of
crankshaft 48 and the other rotating components of the compressor while
eliminating the need to
use counterweights. As a result, the overall height of the compressor
utilizing elliptical cam 46
may be reduced.
[0028] As indicated above, vanes 60 are biased toward the center of cylinder
bore 50 where
they contact exterior surface 66 of elliptical cam 46. Vanes 60 may be coated
with a ceramic or
other material to lessen the friction generated between vanes 60 and the
exterior surface 66 of
cam 46. The contact of the outer surface 66 of elliptical cam 46 with the
inner cylindrical
surface of bore 50 at two circumferentially spaced positions and the biasing
of vanes 60 against
surface 66 forms two working pockets 68 that are defined by vanes 60,
elliptical cam 46 and
cylinder 34.
[0029] Referring to Figs. 3-5, working pockets 68 are sealed on opposite axial
sides thereof by
outboard bearing 40 and main bearing 36. Outboard bearing 40 includes thrust
surfaces 70, 71
upon which elliptical cam 46 is supported. During rotation of crankshaft 48,
elliptical cam 46
bears against and rotates on thrust surfaces 70, 71. The surface of elliptical
cam 46 that contacts
surfaces 70, 71 as well as surfaces 70, 71 and thrust surface 72 (Fig. 8) of
main bearing 36 are
finely machined surfaces that cooperate to seal working pockets 68.
[0030] As shown in Figs. 3 and 7, outboard bearing 40 includes suction
pressure channel 74
formed therein. Channel 74 extends around oil passage 76 formed by boss 73 in
outboard
bearing 40 and is formed as an open channel that is in fluid communication
with bore 50 in
cylinder 34.
[0031] Referring to Fig. 6, as elliptical cam 46 moves in a clockwise
direction, the volume of
working pockets 68 is increased and suction pressure working fluid is drawn
into working
pockets 68. Specifically, suction pressure working fluid passes through
suction port 44 in block
34 to enter the proximal working pocket 68 and suction pressure channel 74. In
order to equalize
the pressure in working pockets 68, suction pressure working fluid is drawn
through suction
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pressure channel 74, passing under elliptical cam 46, around aerodynamically
shaped diverters
78, to enter distal working pocket 68. By utilizing a single suction port 44
to draw suction
pressure working fluid into compression mechanism 32, the cost of machining
and assembling
compression mechanism 32 is reduced. The tapered portions 78 forming the
diverters are
aligned with the longitudinal axis of slot 74 to thereby smooth the flow of
suction fluid around
boss 73.
[0032] As elliptical cam 46 continues to rotate, the portions of cam 46
contacting cylindrical
surface 50 pass vanes 60. At this point, the volume of working pockets 68
begins to decrease,
increasing the pressure of the working fluid contained within pockets 68. As
the volume of
working pockets 68 continues to decrease with the rotation of elliptical cam
46, working fluid
within working pockets 68 reaches a pressure substantially equal to discharge
pressure. Once
that pressure has been reached, flapper valves 82 open and the working fluid
is discharged
through discharge ports 80 (Fig. 5) in cylinder 34 and main bearing 36.
Flapper valves 82, which
are positioned above ports 80, allow for discharge pressure working fluid to
flow into the interior
of housing 12 but operate in a known manner to prevent discharge pressure
working fluid from
reentering ports 80 once discharged. Also shown are valve retainers 84 and
muffler 86.
Discharge pressure working fluid flows past motor 30 and out discharge line
28.
[0033] In addition to, or alternatively to, suction pressure channel 74 in
outboard bearing 40,
main bearing 36 may be provided with a suction pressure channel 88 that
extends between
working pockets 68 and around boss 90 (Fig. 8).
[0034] With reference to Figs. 9 and 10, an alternative embodiment is
disclosed. In this
embodiment, cross passages 94 extending through elliptical cam 96 of
crankshaft 98 allow for
suction pressure working fluid received through suction port 44 to pass
between working pockets
68. Specifically, such pressure working fluid as received through suction port
44 enters the
proximal working pocket 68 and then passes through cross passages 94 into the
distal working
pocket 68. As shown in Fig. 10, cross passages 94 are oriented at a slight
angle relative to the
major chord of the ellipse defined by elliptical cam 96 so that cross passages
94 are never in fluid
communication with the discharge side of the contact points between cam 96 and
bore 50.
Passages 94 and suction pressure channel 70 may possibly be used in
conjunction with one
another or, alternatively, employed separately. For example, in one
embodiment, suction
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pressure channel 74 is present and passages 94 are absent. In another
alternative embodiment,
passages 94 are present and suction pressure channel 74 is absent.
[0035] In addition to the benefits described above, the use of elongate cam 46
also eliminates
the need for an outboard journal bearing. In a typical rotary compressor, the
outboard journal
extends around the oil paddle and through an opening in the outboard bearing.
The interaction of
the journal with the portion of the outboard bearing that defines the opening
prevents off-
centered movement of the crankshaft and eccentric during rotation of the
crankshaft. By
utilizing the elliptical cam of the embodiment of the present invention, the
interaction of
opposing pressure forces on exterior surface 66 of cam 46 substantially
eliminates the need for
an outboard journal on crankshaft 48. By eliminating the need for this
journal, which must be
formed as a highly machined surface, the need to create a correspondingly
highly machined
journal and outboard bearing 40 is also eliminated. As a result, the cost of
manufacturing a
rotary compressor in accordance with this embodiment of the invention is
substantially reduced.
[0036] While this invention has been described as having a preferred design,
the present
invention can be further modified within the spirit and scope of this
disclosure. This application
is therefore intended to cover any variations, uses, or adaptations of the
invention using its
general principles. Further, this application is intended to cover such
departures from the present
disclosure as come within known or customary practice in the art to which this
invention pertains
and which fall within the limits of the appended claims.
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